Abstract
In this study, enhanced oil recovery (EOR) techniques—namely low salinity and nanofluid EOR—are probed at the nanometer-scale using an atomic force microscope (AFM). Mica substrates were used as model clay-rich rocks while AFM tips were coated to present alkyl (-CH3), aromatic (-C6H5) and carboxylic acid (-COOH) functional groups, to simulate oil media. We prepared brine formulations to test brine dilution and cation bridging effects while selected concentrations (0 to 1 wt%) of hydrophilic SiO2 nanoparticles dispersed in 1 wt% NaCl were used as nanofluids. Samples were immersed in fluid cells and chemical force mapping was used to measure the adhesion force between polar/non-polar moieties to substrates. Adhesion work was evaluated based on force-displacement curves and compared with theories. Results from AFM studies indicate that low salinity waters and nanoparticle dispersions promote nanoscale wettability alteration by significantly reducing three-phase adhesion force and the reversible thermodynamic work of adhesion, also known as adhesion energy. The maximum reduction in adhesion energy obtained in experiments was in excellent agreement with existing theories. Electrostatic repulsion and reduced non-electrostatic adhesion are prominent surface forces common to both low salinity and nanofluid EOR. Structural forces are complex in nature and may not always decrease total adhesion force and energy at high nanoparticle concentration. Wettability effects also depend on surface chemical groups and the presence of divalent Mg2+ and Ca2+ cations. This study provides fresh insights and fundamental information about low salinity and nanofluid EOR while demonstrating the application of force-distance spectroscopy in investigating EOR techniques.
Highlights
A suite of techniques for enhanced oil recovery (EOR) involve the injection of fluids into the subsurface to improve overall recovery efficiency of petroleum reservoirs
This paper addresses the two areas by characterizing adhesion forces using atomic force microscope (AFM) between non-polar “oil” compounds with -CH3 and -C6 H5 groups on mica to test for low salinity effects, and interactions between -CH3, -C6 H5 and -COOH terminal groups on mica in different nanofluid solutions
A solution with the same total dissolved solids (TDS) as LS but without calcium or magnesium ions (LSWOMC) was observed to decrease the adhesion force even further, to 318 pN—representing a more than 80% decrease and 70% decrease compared to high salinity effects (HS) and LS cases, respectively
Summary
A suite of techniques for enhanced oil recovery (EOR) involve the injection of fluids (liquid or gas) into the subsurface to improve overall recovery efficiency of petroleum reservoirs. There are several factors that indicate the success of an EOR technique, such as microscopic sweep efficiency, miscibility and wettability. Wettability is one of the most significant phenomena in EOR because it describes the interactions of reservoir fluids, rocks and surrounding thermodynamic conditions. It is the tendency of one fluid to spread on or adhere to a rock surface when at least one other immiscible fluid is present [2]. A reservoir is said to be water-wet when it prefers to contact water in the presence of oil. If oil for a Energies 2020, 13, 4443; doi:10.3390/en13174443 www.mdpi.com/journal/energies
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